Not applicable.
Not applicable.
The present invention relates generally to sheave blocks, such as traveling blocks and crane, or boom, blocks. More particularly, the invention relates to a sheave block having retractable sheave guards.
A xe2x80x9csheave blockxe2x80x9d is an apparatus used in systems for heavy lifting and other weight bearing operations. The sheave block employs numerous xe2x80x9csheaves,xe2x80x9d each sheave having a groove in its outer circumference within which a wire rope, or wireline, may be supported. The sheaves are supported and independently rotatable on a common shaft that extends between opposing side plates, or walls, of the sheave block. Each pass (or loop) of the wireline around a sheave in the sheave block is referred to as a xe2x80x9creeve.xe2x80x9d By passing the wireline around more than one sheave, thus having numerous reeves, the lifting force of the wireline is multiplied.
Some of the most common forms of sheave blocks include traveling blocks used during oil and gas drilling, crane or boom blocks used on large cranes for various heavy lifting operations and pulley blocks. Lifting systems use a power source to create tension in the wireline, allowing the load to be raised and lowered at a certain velocity. Typically, the power source is capable of supplying power within a certain range; thus the power supply is not unlimited.
In certain instances involving the use of sheave blocks, such as in drilling operations, it is desirable to adjust the weight bearing capability of the wireline as the weight of the load changes so as to maintain, or improve, operational efficiency. A well-known method of adjusting the weight bearing capability of a sheave block system is to change the number of reeves of the wireline. This is know as xe2x80x9crereevingxe2x80x9d the wireline. By increasing the number of reeves, the lifting capacity of the system will be increased without additional line tension (or power). At the same time, however, the greater the number of reeves, the slower the lifting operations become at a constant wireline pulling velocity. Thus, while it is sometimes preferred or necessary to increase the number of reeves to lift heavy loads within available power source limits, it is generally desirable to use the smallest number of reeves to lessen the time required for lifting and, thus, to have more time-efficient operation.
During various stages of drilling operations, such as when a heavy drilling string extending deep into the bore hole must be lowered or raised, it is desirable to have a greater number of reeves through the travelling (sheave) block of the drilling rig lifting system to enable the system to support the increased load. At other times, the existence of a relatively light load allows the weight bearing wireline to be reeved over a small number of sheaves in the travelling block, enabling time-efficient operation. The ability to save time by rereeving the travelling block during drilling operations can result in significant cost savings. For example, thousands of dollars per day may be saved when rereeving is used on an offshore drilling rig, where the cost for operating the rig may range between $30,000-$150,000 per day.
Rereeving a sheave block typically involves various design considerations. For example, the sheave block must enable access to the sheaves within the sheave block to allow rereeving. Typically, access is gained by removing or opening safety guards extending at least partially around the sheaves between the side plates. The safety guards are included in the sheave block to prevent the intrusion or entanglement of objects into the sheave block during use and to prevent the wireline from jumping out of the sheave block.
The sheave block design should also allow positioning of the wireline within the sheave block in a load balanced pattern, such as in the center of the sheave block, to assist in maintaining system stability. At the same time, however, it is desirable to minimize the bulkiness and size of the sheave block to enhance handling and installation. Furthermore, because rereeving requires the interruption of the primary operations being performed at the work site, it is highly desirable to minimize the time necessary for rereeving.
Yet another concern is safety. The sheave block should be designed so that the wireline may be rereeved without increasing the risk of equipment damage or human injury.
Sheave block designs that have been proposed in the past have various disadvantages. For example, the increased size and bulkiness of the sheave block disclosed in U.S. Pat. No. 1,577,804 increases its difficulty in use and handling. For another example, the sheave block disclosed in U.S. Pat. No. 2,800,300 must be laid on its side to be rereeved. Rereeving with this block design thus requires substantial time and handling.
Thus, there remains a need for a sheave block that allows speedy rereeving without increasing the risk of safety hazards during rereeving. Especially well received would be a sheave block having sheave guards that generally shield the circumference of the sheaves during lifting operations; that are easily retractable to allow sufficient access to the sheaves for rereeving and positioning of the wireline within the sheave block in a load balanced pattern; that allow rereeving without having to entirely remove the wireline from the sheave block; and that do not add significant mass or size to the sheave block. Preferably, the device should allow the sheave block to perform in a conventional manner. Ideally, existing sheave blocks could be retrofitted, or otherwise adopted, with the new sheave block design.
In accordance with the present invention, there is provided a sheave block for use with a wireline that includes first and second opposing walls and a shaft extending there between. At least one grooved sheave is disposed on the shaft, each grooved sheave being engageable with the wireline. At least one retractable sheave guard is movably connected to the first and second opposing walls and is moveable between open and closed positions, the open position allowing the wireline to be rereeved around at least one of the sheaves without entirely removing the wireline from the sheave block. The retractable sheave guards may be movable between open and closed positions while the wireline is engaged with at least one of the grooved sheaves. Further, the retractable sheave guards may be moveable between open and closed positions without moving the retractable sheave guards upwardly. At least one of the retractable sheave guards may be pivotably moveable between open and closed positions.
The sheave block may include at least one releasable lock capable of retaining at least one of the retractable sheave guards in its closed position. In one embodiment, the lock includes at least one cam rod. At least one of the sheave guards may include a plurality of fingers and a plurality of wireline passages enabling the guard to be movable between open and closed positions while the wireline is engaged with at least one of the sheaves. The fingers may include eyelets engageable with the releasable lock.
At least two of the sheave guards may be connected and may be cooperatively moveable between open and closed positions. At least one coupler connecting at least two of the sheave guards may be included. In one embodiment, the coupler includes at least one link. The sheave block may include at least one sheave guard stop member capable of supporting at least one of the sheave guards in its open position.
In one embodiment, a first sheave guard includes first and second ends, the first sheave guard being moveable downwardly relative to the sheaves from its closed position to its open position. Further, at least one of the first and second opposing walls may include a guide slot, the first sheave guard including at least one guide member moveable upwardly and downwardly within the guide slot. The guide member may be rotatable and include a guide portion having a non-circular cross-section, the guide portion being selectively moveable upwardly and downwardly within the guide slot. The first and second ends of the first sheave guard may be independently moveable upwardly and downwardly relative to the sheaves.
A second sheave guard may be disposed adjacent to the first end of the first sheave guard, and a third sheave guard may be disposed adjacent to the second end of the first sheave guard. The first guard may be connected to the second and third guards. At least one coupler connecting the first guard to the second and third guards may be included. In one embodiment, the coupler includes at least one link. The first, second and third guards may be cooperatively or independently moveable between open and closed positions.
At least one releasable lock capable of retaining the first, second and third retractable sheave guards in closed positions may be included, and the lock may include at least one cam rod. In one embodiment, the releasable lock includes a first rotatable cam rod engageable with the second sheave guard, and a second rotatable cam rod engageable with the third sheave guard. Each of the second and third retractable sheave guards may include a plurality of fingers and a plurality of wireline passages enabling the sheave guards to be movable between open and closed positions while the wireline is engaged with at least one of the sheaves. The second and third sheave guards may be pivotably movable between open and closed positions.
In another embodiment, a sheave block having a housing that contains a plurality of sheaves engageable with a wireline includes first and second side sheave guards and a lower sheave guard, each guard being moveably connected with the housing. The lower sheave guard is disposed between the first and second side sheave guards. Each sheave guard is moveable between an open and a closed position, wherein at least a portion of the guard is farther from the sheaves when the guard is in the open position than when it is in the closed position.
The sheave guards may be movable between open and closed positions while the wireline is engaged with at least one of the sheaves. Further, the sheave guards may be moveable between open and closed positions without moving the sheave guards upwardly. The lower sheave guard may include first and second ends, and may be moveable downwardly relative to the sheaves from its closed position to its open position. The housing may include at least two guide slots, the lower sheave guard including at least two guide members, each guide member being moveable upwardly and downwardly within one of the guide slots. Each guide member may be rotatable and include a guide portion having a non-circular cross-section, the guide portion being selectively moveable upwardly and downwardly within one of the guide slots.
The lower sheave guard may be connected to the first and second side sheave guards. At least one coupler connecting the lower sheave guard to the first and second side sheave guards may be included. In one embodiment, the coupler includes at least one link. The first and second side sheave guards and the lower sheave guard may be cooperatively or independently moveable between open and closed positions.
At least one releasable lock capable of retaining the sheave guards in their closed positions may be included, and may include at least one cam rod. The releasable lock may include a first rotatable cam rod engageable with the first side sheave guard, and a second rotatable cam rod engageable with the second side sheave guard. Each of the first and second side sheave guards may include a plurality of fingers and a plurality of wireline passages enabling the sheave guards to be movable between open and closed positions while the wireline is engaged with at least one of the sheaves. The sheave block may include at least one sheave guard stop member capable of supporting at least one of the sheave guards in its open position.
In another embodiment, a sheave block for use with a wireline includes first and second opposing walls, a shaft extending between the walls and having at least one grooved sheave disposed thereon. Each grooved sheave is engageable with the wireline. A plurality of retractable sheave guards movably connected to the opposing walls is included. This embodiment also includes means for movably connecting the retractable sheave guards to the walls to allow the sheave guards to be moved between open and closed positions while the wireline is engaged over at least one of the sheaves, the open positions allowing the wireline to be rereeved around at least one of the sheaves without entirely removing the wireline from the sheave block. Also included is means for guiding the retractable sheave guards between open and closed positions. The sheave block may further include means for connecting the retractable sheave guards together.
Further in accordance with the present invention, a method of rereeving a wireline through a sheave block without having to completely remove the wireline from the sheave block is included. The sheave block includes a plurality of sheaves, at least one retractable sheave guard movable between open and closed position and at least one releasable sheave guard lock releasably securing the retractable sheave guard in the closed position. The wireline passes through the sheave block and is reeved over at least one sheave in the sheave block. The method includes releasing at least one sheave guard lock, moving at least one retractable sheave guard into an open position without disturbing the wireline passing over at least one sheave in the sheave block, moving a free end of the wireline through the sheave block to change the number of reeves of the wireline over the sheaves in the sheave block, moving the retractable sheave guard(s) into a closed position, and locking the sheave guard lock(s). The method may also include moving at least one reeve of the wireline from one sheave to another sheave in the sheave block.
Thus, the present invention includes the use of sheave guards that can safely and easily be moved between opened and closed positions to enable efficient and quick rereeving and positioning of the wireline in a load balanced pattern in the sheave block without having to remove the entire wireline from the sheave block. The present invention facilitates rereeving without the assembly or disassembly of numerous complex parts. Further, the present invention may be used with various types of sheave blocks, or mechanism, having numerous sheaves, such as traveling blocks and crane blocks, without significantly adding to the size of the block.
Accordingly, the present invention has advantages which enable it to substantially advance the technology associated with sheave block devices and methods of rereeving. The characteristics and advantages of the present invention described above as well as additional features and benefits will be readily apparent to those skilled in the art upon reading the following detailed description and referring to the accompanying drawings.